The present invention relates to a combined magnetic write and read head for a recording medium which is provided with at least one magnetizable storage layer, into which information can be written along a track by perpendicular or vertical magnetization of the storage layer. Such magnetic heads comprise a ring-head-like magnetic conduction body for carrying the magnetic flux, the conduction body having two magnet legs, the poles of which are arranged in tandem as viewed in the direction of motion and which are arranged at a predetermined spacing from each other, with at least one coil winding associated therewith, the turns of which extend through a space formed between the magnet legs. Such magnetic heads are described in DE-OS 29 24 013 or U.S. Pat. No. 4,287,544.
The principle of perpendicular magnetization for storing information is generally known. See, for instance, IEEE Transactions on Magnetics, vol. MAG-16, no. 1, January, 1980, pages 71 to 76, or the above mentioned patent literature. For this principle, which is frequently also called vertical magnetization, special recording media in the form of rigid magnetic storage discs, flexible individual discs (floppy discs) or magnetic tapes are required. Such a recording medium has at least one magnetizable storage layer of predetermined thickness which contains a magnetically anisotropic material, especially of a CoCr alloy. The axis of the so-called easy direction of a magnetization of this layer is oriented perpendicularly to the surface of the medium. By means of a special magnetic head, the individual bits of information are then written along a track in successive sections, also called cells or blocks, by suitable magnetization of the storage layer. In practice, the changes of the magnetic flux, i.e., the transitions from one direction of magnetization to the opposite one, are used as information. The sections have a predetermined dimension in the longitudinal direction of the track, also called wavelength. This dimension can be substantially smaller than the limit which is given, in the method of longitudinal or horizontal storage, by demagnetization. Thus, the information density in the recording medium can be increased advantageously by the principle of vertical magnetization.
However, the write and read heads known for the principle of longitudinal magnetization, i.e., heads with which the write as well as read function can be carried out, cannot be used directly for vertical magnetization. If these heads are used, which generally have a ring-like shape, in fact the flux conduction which is also desired with the principle of vertical magnetization, to form a circuit closed as far as possible and with low magnetic resistance, can be achieved, but writing of both poles of these ring heads can hardly be suppressed, so that corresponding difficulties in reading the recorded information result.
One is therefore compelled to develop special combined write-read heads for the principle of vertical magnetization. A magnetic head suitable for this purpose has in general a so-called main pole, by which a vertical magnetic field strong enough for reversing the magnetization of the individual sections of the storage layer is produced. The necessary magnetic return path can then be accomplished, for instance, by a so-called auxiliary pole on the opposite side of the recording medium. See the mentioned literature reference, IEEE Trans. Magn. vol. MAG-16. In addition, a return by a stray flux also is known. See IEEE Trans. Magn., vol. MAG-18, no. 6, November, 1982, pages 1170 to 1172. A magnetic return can further be accomplished by a separate auxiliary pole which is located on the same side as the main pole. See IEEE Trans. Magn., vol. MAG-17, no. 6, November, 1981, pages 3120 to 3122 or vol. MAG-18, no. 6, November, 1982, pages 1158-1162, or the mentioned patent literature. Accordingly, the magnetic write and read head known from the above patent literature contains at its front, as seen in the direction of motion of the recording medium moving under it, the auxiliary pole and on its back side the main pole proper. This main pole is formed by a magnet leg which comprises substantially a magnetic layer which extends perpendicularly to the direction of motion and which is applied to a nonmagnetic substrate. The auxiliary pole, which is substantially longer in the direction of motion and which is located in front of the main pole, is formed by a magnet leg which is composed of several magnetic layers arranged perpendicularly to the direction of motion with interposed insulating layers. Between this auxiliary pole, which thus covers a comparatively much larger area of the track as the main pole, a space or air gap, several .mu.m wide, is formed. In this air gap is disposed an electric winding, by which the main pole can be excited for the write function, and the excitation of the main pole can be registered for the read function. Because of the relatively large write current required, this winding must have accordingly large conductor cross sections, however. Since, however, the space between the main and the auxiliary pole is very small, the number of turns of the winding and consequently, the read voltage, are limited accordingly. The auxiliary pole should in any case serve only for returning the magnetic flux. A possible concurrent writing of the auxiliary pole can possibly be tolerated, since the recording main pole always lags it and therefore overwrites information which may have been written by the auxiliary pole. However, it is a prerequisite that the width of the auxiliary pole be not greater than that of the main pole and therefore, already written adjacent tracks remain uninfluenced. With this known magnetic head, also a relatively large width of the air gap is called for as compared to the main pole, besides the larger cross section of the auxiliary pole as compared to the main pole, so that a far-reaching reduction of the magnetic flux density at the auxiliary pole can be assured. Even so, the air gap of the known magnetic head cannot be made so wide that concurrent reading of the auxiliary pole by its trailing edge can be suppressed completely. This can lead to difficulties in information detection.
The remaining space of the air gap which is not filled by the electric winding in the known magnetic head and which faces the recording medium must be filled with a so-called insulating gap layer. This gap layer should comprise material as hard as possible such as Al.sub.2 O.sub.3 in order to avoid notches or washouts during the manufacture of the head, since such unevenesses can lead to crashing of the magnetic head, which is guided above the recording medium with extremely little spacing, by embedded dirt particles. However, it has been found that this gap layer between the main and the auxiliary pole is extremely difficult to make if relatively large gap widths are required, as with the known magnetic head.
Due to the difficulties encountered with the principle of vertical magnetization in reading with the known combined write and read heads, it has been proposed to carry out the write and read functions also with separate heads, so that these heads can be adapted optimally to the respective function. See, for instance, IEEE Trans. Magn., vol. MAG-16, no. 5, September, 1980, pages 967 to 972. For reading, the ring heads known per se from the principle of vertical magnetization can be used, while writing can be carried out with special heads. Such a write head has, for instance, on its side facing the storage layer of the recording medium, a main pole, also called a single-pole head, with a longitudinal dimension of, for instance, 3 .mu.m, opposite which is located on the back side of the recording medium a substantially larger auxiliary pole. The second head, which is required only for reading, is a known ring head and has a gap width of, for instance, 0.2 .mu.m. See, IEEE Trans. Magn., vol. MAG-17, no. 6, November, 1981, pages 2538 to 2540. Such systems for reading and writing with separate, special heads adapted to the respective function, however, are relatively elaborate as far as the mechanical design is concerned.